Process of treating lead sulphide ores



Dec. 5, 1933. N. c. cHRlsTENsEN 1,937,635

PROCESS OF TREATING LEAD SULPHIDE DRES Filed Sept. 29, 1931 fotaolz oll Nasi@ vPatented Dec. 5, 1933 l PROCESS F TREATING LEAD ASULPHIDE ORES Y Niels C. Christensen, Salt Lake City', Utah Application september 29, 1931 Serial No. 565,861

13 claims. (c1. 23-127) This invention relates to a process for the treatment of lead sulphide ores or concentrates for the recovery of lead therefrom as metallic lead or lead products.4 The process consists of 1 four main steps or parts, the converting of the lead in the ore to lead sulphate, the extraction of the lead from the sulphated ore by leaching with hot concentrated brine, the precipitation of the lead from the brine, and the treatment oi the precipitated products for the recovery of metallic lead or for the making of marketable lead products.

It is well known that lead sulphide may be converted to the sulphate by a suitable roasting operation or by treatment with hot concentrated sulphuric acid containing over 90% HzSOi.

The sulphatizing roast is however not an entirely .satisfactory operation dueto dust loss, incomjplete ysulphatization, 'loss by volatilization, and "i the necessity oi oxidizing the other sulphides,

such as pyrite mixed with the lead sulphide.

.Treatment with an excess of hot sulphuric acid of high concentration results `in a high acid con-l sumption due to the reduction-o1" the acidby the sulphide and the reaction between the freed sulphur and the hot acid as indicated in the following equations:

These two actions taken together would represent, -as the complete action taking place un der such a process, the following:- n

3PbS+12H2SOi=3PbSO4l12SO2+12H2O Or in other words only one fourth of the sulphuric acid used goes into the lead sulphate formed, and much water is evolved which serves no useful function but dilutes the excess acid used and has to be gotten rid of by subsequent costly evaporation (i. e. this dilute acid requires concentration todrive on vthis relatively large amount of water). l

sulphuric acid 'of 60%, even at the boiling point has no substantial sulphating action on galena. sulphuric acid of 70% at the boiling point acts only with extreme slowness on galena and even acid of this concentration,l at'the boil-U ing point is to some extent reduced by the HZS liberated, causing a loss of acid. With acid of 86% concentration at the boiling point, the sulphating action is somewhat more rapid, but the amount of reduction of H2804 by I-IzS is also increased. The boiling points of the acid increase with the concentration, and the vproportion of H2504 reduced, likewise increases the concentration of the acid used. Y

An important object Vofzthe present invention is to sulphate the leadcontent of galeria with II2SO4 of only 60 to 70% concentration, and to accomplish this result without the reduction of any material proportion of the sulphuric acid by HzS and also to recover practically vall lof the sulphur content of the galeria, in the form of B2S whereby the latter is not wasted in the re'- duction of H2SO4. The sulphur thusforined is mixed with the treated ore and requires special treatment if it is to be recovered. Treatmentl with acids of such high concentration also involves a considerable concentrating operation to recover the excess acid and also involves some diiculty and danger in operation. The present invention aims to sulphate the lead and recover thesulphur as H by treatment with sulphuric acid of such lower concentration that substantially no free sulphur is `formed, avoids the necessity for highconcentration of the excess acidused, land avoids much of the danger and difficulty involved in handlinghigh- Yly concentrated acid. It also avoids waste of sulphuric acid by reduction to S and SO2.

Itis stated in my U. S. Patents 1,434,084 and 1,435,699, hot sulphuric acid of a concentration between %r and 70%does not attack or'dissolve'v galena to any appreciable extent. I havefound however that sulphuric acid of this strength does attack galeria supercially, the acidi reacting upon only the surface of the galeria particlesy to form a very thin superficial coating of PbSO4 and drive orf the sulphur in attacked galeria as'indicated in the following equation: f

The lead sulphate thus formed beingpractically' insoluble in sulphuric acid of this concentration is not dissolved and protectsthe remainder of the coated particle against further action by the acid. I have found howeverthat bygrinding the ore while treating it with the hot sulphuric acid of this concentration thatthe` galena may be completely converted-to the sulphate and .all the sulphur be driven' off asHzS as indicated in the foregoing equation, the grinding or attrition rub.-A bing the sulphate coating from the galena particles and allowing the reaction to go to completion. The importance of this discovery will be apparentv from the followingfacts. In the prior art it has always been thought necessary to use hot acids of much higher concentration` i. e;

.from to 95% H2SO4. The use of such con-v with A ics ric

centrated acid results in a very high acid consumption due to decomposition of the sulphuric acid `and formation of sulphur and SO2 irldicated in the following equations:

`The practical diiiiculties involved in handling the concentrated acid are also very great as com-l pared with the handling of `acids containing from to 6.5%7H2SO4 such as are preferred in this process. In the earlier processes using the concentrated acid the sulphur combined with the lead in the galeria could not be economically ree covered since it was obtained either in the form of lfree sulphur mixed with the ore residue or was driven of in the forni of SO2 (by reduction of HzSOi). In the present process the sulphur' is driven off as l-I2S from which the sulphur may befreadily recovered at a low cost. The very large saving inl acid consumed,V the greatly increased ease of operation and the recovery of the sulphur in a form suitable for its recovery are all features of such practical valueias to make this invention a radical improvement in theV art. The lead sulphate formed in the process, is dissolved away from the ore residue by leaching with a sodium chloride brine, the sulphate as is well known, being soluble in sodium or .calcium chloride brines. The method of vrecovering the lead Yfrom this solution and the treatment of the precipitate depends upon the final product desired as described below. "As compared. with the above describedV old process, the present process requires only one moleculev of sulphuric acid, per molecule of PbS, Whereas'the older process required four molecules of the acid per molecule. or Phs. And further in the said new process, there is no water given off to cause dilution of the sulphuric acid. Al further. important advantage of the present process is the possibility of using sulphuric acid of about :concentratiomwhereas in my said prior patent,.sulphuric acid. oi about 86% as a minimum is needed for approximately complete sulphation of the lead.

The 'accompanying flow sheetxillustrates the `practical application oi the process as described in theV following.

The vfirst and essential step of the process, the sulphating of the galeria and driving-off of the sulphur as H25 is carried out by grinding the ore from 15to3o minutes with sufficient excess of hot sulphuric acid of a concentration between 6i) and 75%, preferably approximately v65% to make a fluid pulp. This operation is preferably carried out in a properly acid-proofed pebble mill having a silex or porcelain lining and supplied vith flint pebbles or porcelain marbles as a grinding medium. This apparatus is called the sulphator (1) in the followingdescription. To pre; vent contamination of the H253 the acid and ore are preferably sentinto Vand discharged from the mill through suitable air-tight glands. In the treatment of` some ores the-lead maybe partially sulphated with acids of a concentration as low as 50% but for complete sulphating in a short period 65% acid is preferred. The acid consumed in the sulphating, operation may be added as 98% acid in order to avoid excessive evaporation in the'process, but this acid should bemixed with the circulating'acid before coming into contact rwith the ore inr order to avoid loss of acid and H25 dueto the reaction between the ore and highly concentrated'acid as noted above. Acids recovered and utilized as described therein, or ifV present in small quantity may be recovered as described below. Pyrite and chalcopyrite, (as previously noted in my U. S. Patent 1,434,084) vandthe silver sulphide minerals may be mostly left unattacked by sulphuric acid of the strength esV used in this process. The sulphated ore and eX cess of hot acid from the sulphator (1) goes te the lter (2) where the excess oi circulating acid is filtered out and passed through the heater and concentrator (5) and used over again in the treatment of more creas shown. rIfhe acidfilter caire fro-rn the lter (Z) is washed free of acid (and zinc sulphate il. the ore contains Zinc) Vpref-- erably in a counter-current washer (3) and iilter (d) as shown. The acid solution (containing anyY anic in the ore) from this washing operation may bepassed through theY cohcentrator and heater (5) (along with the circulating acid) and the water is evaporated oli to `make acid of the ren quired concentration.l This concentrating operation precipitates the zinc sulphate which may be in solution which is filtered out in the filter (6) and the hot acid'sent to the sulphator for reuse.

The washed lead sulphate and ore residue-*from the lter (e) is treated with hot concentrated sodium chloride brine containing CaClz, from the precipitation of the lead in a previous cycle, inv

the leaching agitator (7).

solution and' precipitating calcium Ysulphate vas indicated in the following equation:

from the agitator (7) tothe dewalterer (8). where the pregnant solution is separated andsentto the precipitating department. The ore residue from the dewaterer (8) is washed first with hot barren brine and then with hot water in the counter-current washer (Q) land filter (1G) the wash solutions 'being mixed Withrthe pregnant brine;` and sent to the lprecipitating department and the ore residuer to flotation for recovery oi pyrite, and the gold and silver, etc.l Y z The leaching operation in the agitator ('7) may be conducted with a neutral brinev ifit is not desired to dissolve any silver at this stage of the oretreatment. If it is desired to recover 'as much silver as possible the agitator, suflicient acid v Thelead sulphate isy dissolved in the brine forming lead chloride in,

may be added at the beginning of the leaching operationjto bring the soluble silver into solution.

' The excess acid isthen neutralized at the end of the leaching operation by the addition of oxiu dized lead ore, as noted above. f

The hot pregnant solutions from the dewaterer (S) and washer (9) are mixed and, ifV any silver is dissolved, treated with, metallic lead (preferably lead dust) in the precipitatorv (11) torremove ide.

the silver (and copper if any is present) and the precipitate and excess lead dust is filtered away from the solution in the filter (12). If no silver or copper is present in the solution at this point this precipitation step and the precipitator (11) and iilter (12) may be eliminated. If desired the silver (and copper) brought into solution in the agitator (7) may also be precipitated lat the end of the leaching treatment by the addition of a small amount of lead dust or soluble sulphide (such as Ca(SI-I) 2) at the end of the leaching operation, the metals thus being precipitated in the pulp and later recovered in the flotation treatment of the ore residue. If this-method is used the precipitator (11) and filter (12) would be eliminated.

The recovery of the lead from pure pregnant brine prepared by any one of the foregoing methods may be carried out to make lead bullion as shown in the flow sheet from A to A, or for the manufacture of lead pigments by the methods illustrated in the fiow sheet in the flow line-B- B-B-B. By the rst method (A-A) all the lead is precipitated from the pregnant solution by agitation with lime or calcium hydroxide in the precipitatcr (13), the lead being precipitated mainly las a hydroxide with the formation of CaClz in solution as indicated in the following equation The precipitate is not a pure hydroxide, however, as shown in the equation but contains some hydroxychloride and unconsumed calcium hydrox- A substantially complete precipitation-may be secured with considerably less than a chemical equivalent of lime to lead but since an equivalent of lime to lead is necessary for the recovery of the lead in the furnace (15) it is preferred to add the full amount of required lime at this point. The hydroxide precipitate is separated from the barren solution by filtration in the filter (14) and (preferably after drying) is mixed with carbon and heated to a red heat in the furnace (15) to reduce the lead to metallic form (or is heated with any other suitable reducing agent such as natural gas to form metallic lead) The hydroxychloride and unconsumed lime in the precipitate react in the smelting treatment to give metallic lead and a small amount of calcium chloride slag which is added to the leaching solution for removal of the sulphate as described above. The smelting or reducing operation may be carried out in a blast furnace (or retort if desired) but smelting in a reverberatory furnace with a slag or cover consisting of a mixture of calcium chloride and sodium chloride is preferred, as briquet-- ting of the precipitate is not required for this treatment and volatilization vloss is less than'in the blast furnace. Little' or no washing ofthe lead precipitate is required in tlfie'iilterv (14) as the salt and CaClz in the filter cake is recovered in the slag from the furnace (15) and returned to the leaching circuit.

If the lead is to be recovered asa paint pigment of other lead products, the precipitation and subused over again yin the treatmentof mor`ev'sul-'-` Dhated ore as described. t

The lead hydroxide precipitate from the filter (14) and the PbClz from the filteril'?) are utilized to make the desired lead 4pigments briefly described below. To make basic lead carbonate` (white lead) (the lead hydroxide precipitate and.

the lead chloride are used in the ratio of one molecular weight vof lead hydroxide to two molecular weights of lead chloride and mixedwith finely divided CaCOs in the ratio of two molecular weights. -This Vmoistened mixture is ground -to-- gether in the grinderor pebble mill' (18) and thereaftertreated with water (preferably hot) in the agitator or treater (19). This treatment results in the formation of basic lead carbonate according to the reaction shown in the following equation:

The CaClz isv washed out of the precipitate in the treater preferably by counter-current treatment with water'during the conversion to the basic carj bonate, and the basic carbonate is filtered in the.Y iilter (20) and dried or emulsiii'ed with oil to make the finished white lead pigment.- The product made in this manner is of excellent quality as toY color, tinting strength, and covering power being superior to most of the white lead produced by treatment of metallic lead by the methods now in common use. By Varying the proportion of Pb(OI-I)2 precipitate to PbClz and CaCOa in the foregoing treatment white lead products of any desired ratio of Pb(OH)2 Yto PbCOz may beobtained.

If it is desired to make a basic leadsulphate mixture, the procedure is similar to the foregoing i' except that CaSO4 is substituted for CaCOs in the mixture. `In this treatment of the mixture ther Pbciz reacts with the Caso) to formr'bsoiand CaClz as indicated in the following. equation:

pbolz'rcasopPbsoi-kcacu The CaCl2 is washed out of the precipitate as previously described leaving a mixture rof. the

Pb(OH) 2 and PbSO'l in the desired ratio.

If desired the PbClz may be mixed with th CaCO3 or the CaSO4 and ground and treated water to make the' normal carbonate or sulphate as indicated below:

l Y Pbc12+caco3=pbco3+cac12 l i Pbc12+casoir=rbso4+`cao12 and the PbCOa and PbSO4 may then vbe mixedwith the desiredproportion of the lead hydroxide precipitate and ground and treated with water to form the desired basiccarbonate basic sulphate mixture. Y f To make lead hydroxychloride, the lead chloride from the. filter (17) is mixed with the, lead hydroxide precipitate from the filter V(19) 'and or the desired ground together and treated with water to remove'j the CaClz. By this treatment lead hydroxychloills Cal

ride is formed according jto the followingequation: Pb on) 2+Pbo12`=2rbonci droxychlorides containing any desired proportion of hydroxide to chloride may be secured. The normal hydroxychloride PbOiClis a white pigment of highV hiding power and tinting strength,v though the color is not as white as the basic car-A bonate, inclining to a yellowish tinge. 'Y Hydroxychlorides with greater proportions of the hydroxide are more yellow'with increase inhydroXide-and with two parts of hydroxide to one oipchloride are a'bright yellow. .f

The process as described abo-ve is applicable to all types of lead sulphide ores and concentrates, both simple lead sulphide ore and` so called cornplex sulphide ores of lead and zinc or lead, Zinc and'copper. VIts application to the latter type oi ores ris more fully disclosed and claimed in my copending application 568,514. f I

Thel methods and apparatus described in lthe foregoing are merely those preferred at the present time` for carrying out the process in commercial operation. Other forms of apparatus and rvariations in method may be successfully usedy incarrying out the process either as a batch or as a continuous process and it is therefore not desired to restrict the invention only to the appav-ratus and methods ldescribed above.

In my concurrent application 565,862, containingisubstantiallyrthe same disclosure as the present casefI have claimed theproduction of lead pigments as rdescribed herein.

i -Having describedmy invention what I claim not below 60% l-lzSQi, in proportions suiiicient said treatment, and thereby Yconverting the lead and using it '5 Y to -forrn a flowable pulp but the amount of said sulpl acid being insufficient tordissolve any largerrraction ofY the whole of the lead sulphate' formed, "maintaining the materials hot during.

vsulphide tovlead sulphate and driving off the sulphur as V H2S, and 'Filtering and Washing said excessy acid away from said lead sulphate and residue otore and concentrating andheatirlg vsaid in the treatment' of more ore 3. rlhe process of treatina ores and ore concen- V tratescontaininglead sulphide whichrconsists in grinding said ores land concentrates with hot sulphuric acid of a concentration above 60%' and bolos/'770% HZSCM at a temperature near the boiling point of said acid, and` thereby converting ther lead sulphide to leadsulpl'iate and driving; ofi the sulphur as H28, and filtering andwaslfiingV said" excessv acid away 'from said vlead sulphate and residueof ore `and concentrating and heating said acid and using it in the treatment of more ore material. 5

4. The process oftreating ores and ore `con' centrates containing lead sulphide which consists in grinding said ores andconcentrates with hotsulphuric acid of ai concentration. above 60% "andl 5; The process-of treating ores and ore concen-r tratesl containing lead sulphide which consists in grinding said ores andthe like with an excess of hot sulphuric'acid of such concentration that the lead sulphide isv converted to lead sulphate and the sulphur is-.driven oli as HzS, and filtering and washing` said excess acid away from saidlead sulphide and residue of ore and concentrating and heating said acidandusing it in the treatment of more orernaterial, and dissolving said lead` sulphate in a hotconcentrated sodium chloride brine containing calcium chloride from a previous operation and separatingrsaid pregnant brine from the residue of ore, and precipitating the lead from said hot-pregnant brine with'v calcium hydroxide and forming calcium chloride in said solution and ltering out the lead hydroxide precipitate thus formed and using the barren. brine thus forined in treatment of more sulphated ore material.

6. The process of treating ores and` ore concentrates containing lead sulphide which consists los in grinding said ores and the like-with'an excess brine from the residue of ore, andprecipitating the lead from said hot pregnant brine with calcium hydroxide and forming calcium chloride in:

saidsolution and iiltering` out the lead hydroxide precipitate thus formedl and using the barren .brine thus formed in treatmentof more sulphated ore material.

7. The process of treating ores and ore concentrates containing lead sulphide which consists in l grindingv said ores and4 concentrateswith hot sul,- phuricacid of a concentration between 60% and '70% H2504l and thereby converting the lead sulphide-to lead sulphate and driving off the sulphur as I-IQS, and iiltering and washing said excess acid away from said-lead ,sulphate and residue of ore and concentrating and heating said acid and using it in the treatment or" more ore 'materiaLand' dissolving Asaid lead sulphate in a hot concentrated sodium chloride'brine containing calcium chloride fromv a previous operation and separating saidf pregnant brine from the residue of ore, and precipitating the lead from said hot pregnant ,solue tion'with-calciurn hydroxide and formingcalcuin chloride in said solution and iiltering out'the lead sulphated ore material.

8. The process oi treating ores and ore concen-V trates containing lead sulphide Which consists in grinding said ores and concentrates withhot sul- Yhydroxide precipitate thus formed and using the barren'brine thus formed 'in treatment of morev phuric Vacid of a concentration between 60% and 70% H2804 at a temperaturenear theboiling pointvof said acid, and therebyconverting the lead sulphide to lead sulphate and driving off the sulphur as H25, and filtering and washing said excess acid away from said lead sulphate and residue of ore and concentrating and heating said acid and using it in the treatment of more ore material, and dissolving said lead sulphate in a hot concentrated sodium chloride brine containing calcium chloride from a previous operation and separatingr said pregnant brine from the residue of ore, and precipitating the leadfrom said hot pregnant brine with calcium hydroxide and forming calcium chloride in said solution and iiltering out the'lead hydroxide precipitate thus formed and using the barren brine thus formed in treatment of more sulphated ore material.

9. The process of treating ores and ore concentrates containing lead sulphide which consists in grinding said ores and the like with anexcess of hot sulphuric acid of such concentration that the lead sulphide is converted to lead sulphate and the sulphur is driven oi as H25, and ltering and washing said excess acid away from said lead sulphate and residue of ore and concentrating and heating said acid and using it in the treatment of more ore material, and dissolving said lead sulphate in a hot concentrated sodium chloride brine containing calcium chloride from a previous operation and separating said pregnant brine from the residue of ore, and precipitating the lead from said hot pregnant brine with calcium hydroxide and forming calcium chloride in said solution and filtering out the lead hydroxide precipitate thus formed and using the barren brine thus formed in treatment of more sulphated ore material, and heating said lead precipitate with a reducing agent to make metallic lead.

10. The process of treating ores and ore concentrates containing lead sulphide which consists in grinding said ores and the like with an excess of hot sulphuric acid of a concentration between 50% and 75% H2504L and thereby converting the lead sulphide to lead sulphate, and filtering and washing said excess acid away from said lead sulphate and residue of ore and concentrating and heating said acid and using it in the treatment of more ore material, and dissolving said lead sulphate in a hot concentrated sodium chloride brine containing calcium chloride from a previous operation and separating said pregnant brine from the residue of ore, and precipitating the lead from said hot pregnant brine with Vcalcium hydroxide and forming calcium chloride in said solution and ltering out the lead hydroxide precipitate thus formed and using thebarren brine thus formed in treatment of more sulphated ore material, and heating said lead precipitate with a reducing agent to make metallic lead.

'11. The process of treating ores and ore concentrates containing lead sulphide which consists in grinding said ores and concentrates with hot sulphuric acid of a concentration between 60% and 70% H2504 and thereby converting the lead sulphide to lead sulphate and driving off the sulphur as H25, and Afiltering. and washing 'said excess acid away from said lead sulphate andY residue of ore and concentrating and heating said acid and using it in the treatment of more ore material, and dissolving saidv sulphated ore material, and heating said lead' precipitate with a reducing agent to make metallic lead. l

12. 'Ihe process `of treating ores and ore concentrates containing lead sulphide which consists in grinding said ores and concentrates with hot sulphuric acid of a concentration between 60% and 70% H2504 at a temperature near the boiling point of said acid, and thereby convert- 'ing the lead sulphide to lead sulphate and driving off the sulphur as H25, and ltering yand Washing said excess acid away from said lead sulphate and residue of ore and concentrating and heating said acid and vusing it in the treatment of more ore material, and dissolving said lead sulphate in a hot concentrated sodium chloride brine conice taining calcium chloride from a previous opera-v l tion and separating said pregnant brine from the residue of ore, and precipitating thelead from said hot pregnant brine with calcium hydroxide and forming calciumv chloride in said solution and iiltering out the lead hydroxide precipitate thus formed and using the barren brine thus formed in treatment of more sulphated ore material, and heating said lead precipitate `4`with a reducing agent` t0 make metallic lead.

13. The process of treating ores and ore concentrates containing lead sulphide, which consists in grinding said ores and concentrates with hot sulphuric acid of a concentration not below about 60%'1-1'2504 and not substantially above 65% H2504, and thereby converting the lead 'sulphide into lead sulphate and driving off the sulphur as H25.

NIELS C. CHRISTENSEN. 

